1. Field of the Invention
The present invention relates to a positive-working light-sensitive composition which can be used for making lithographic printing plates, proof sheets for process printing and diagrams for overhead projectors as well as for forming fine resist patterns during the production of semiconductor integrated circuits.
2. Prior Art
As light-sensitive substances which are used for making a lithographic printing plates and the like and solubilized by irradiation of actinic light rays (so-called positive-working light-sensitive substances), there have been known orthoquinone diazide compounds and, in fact, they have widely been used for making lithographic printing plates and the like. These light-sensitive substances make use of the properties of the orthoquinone diazide compounds that they are decomposed into 5-membered carboxylic acids through the irradiation of actinic light rays and are consequently made alkali-soluble, but the sensitivity thereof is still insufficient. This is because the optochemical sensitization of these compounds is highly dependent upon the kinds thereof and the quantum yield thereof never exceeds 1. Moreover, they can be sensitive only to light in a specific wavelength range and, therefore, they have poor adaptability to a variety of light sources and it is difficult to impart white light safety. Furthermore, they cannot be used in applications in which light having a short wavelength is used for the improvement in resolution of photoresists since they highly absorb light of the Deep-UV region.
Recently, there have been proposed several new positive-working light-sensitive materials which can supersede the orthoquinone diazide compounds. An example thereof is a polymeric compound carrying o-nitrocarbinol ester groups such as disclosed in U.S. Pat. No. 3,849,137. However, this polymeric compound does not exhibit sufficient sensitivity either.
Further, there have also been known positive-working light-sensitive compositions which comprise compounds generating acids by irradiation of light, compounds which are, for instance, hydrolyzed by acids and cause a change of solubility in an alkaline water and optionally other additives such as binder resin. Such compositions are disclosed, for instance, in U.S. Pat. Nos. 3,779,778, 4,101,323, 4,247,611, 4,248,957, 4,250,247 and 4,491,628. However, all of these light-sensitive compositions have low sensitivity, show only a small difference between the solubilities of exposed portions and unexposed portions or provide insufficient patterned shapes of positive images and, therefore, they have not yet been practically used.